Networked desktop computing is typical in both the office and home. Networking of mobile devices, such as mobile telephones, laptop computers, headsets, and PDA's (Personal Digital Assistants), is more difficult. One problem has been that there has not been a commonly accepted standard approach for attaching such devices, such as the mobile equivalent of a LAN (Local Area Network) card or a modem, to a WLAN (wireless LAN).
Bluetooth (BT) is a low cost wireless connection technology. The Bluetooth technology is described in the Bluetooth specification version 1.1, available from Bluetooth SIG, Inc. (see also the www.bluetooth.com web site.) This technology provides for a common attachment approach for different devices, and so enables mobile phones, laptops, headsets, and PDA's to be easily networked in the office and eventually in public locations. Other standards such as the IEEE 802.11 (Institute of Electrical & Electronics Engineers) and ETSI (European Telecommunications Standards Institute) HIPERLAN/2 provide a generally similar connection function as Bluetooth and may be used to support WLAN (see the IEEE 802.11 “Wireless LAN Medium Access Control (MAC) and Physical Layer Specifications” and ETSI specifications for HIPERLAN/2 such as ETSI document number TR 101 683, “Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; System Overview”).
Wireless LAN (WLAN) access points (LAP's) such as those used by 802.11 and Bluetooth are part of an IP subnet; that is, a range of IP addresses that are normally used by all the devices connected to a section of the network delineated by a router (which may also be known as a gateway), direct packets to and from devices that are outside the subnet.
In one conventional approach, devices (e.g., a router, gateway, or mobile devices) inside the subnet are primarily identified by their MAC address. This is a fixed address tied to the Ethernet card. IP addresses are associated with MAC addresses. There can be multiple IP addresses associated with a single MAC address. Each router or gateway device on the subnet maintains a cache which maps IP addresses within the sub-net to the associated MAC addresses. Data packets are sent to the MAC address associated with the IP address by the cache. (For destinations outside the sub-net the data is sent to the router which then forwards them.)
In order for a device (e.g., router or gateway) to find the MAC address associated with a particular IP address, an ARP (address resolution protocol) is used. The device (e.g., router or gateway) follows the ARP and sends out a broadcast message asking for the device associated with the included IP address to respond with its MAC address. Once received it is added to the cache.
For a situation where there are mobile devices attached to an access point then the mobiles MAC address is associated with an IP address from within the subnet IP address space. If the mobile device moves to another access point that is in the same subnet then all that is required is for the new access point to realize that it must respond to the MAC address of the mobile device that has just associated itself, and the previous access point to cease to response to that MAC address. The MAC to IP address cache does not need to be changed.
If, however, the mobile device moves to an access point connected to another subnet then the local MAC to IP cache does not apply. The mobile device would typically be required to obtain a new IP address and so break the previous connection. The user of the mobile device is typically re-required to re-establish a stateful end to end connection such as IPSec (IP Security Protocol, an encryption protocol from the Internet Engineering Task Force (IETF), an organized activity of the Internet Society), and so the user may be required to re-register with the WLAN. For example, the user may be required to re-enter a PIN (personal identification number) when connecting to a new subnet.